Emissivity of Surface Table- Heat Transfer

Emissivity of Surfaces Table - Heat Transfer

Heat Transfer Engineering
Thermodynamics

Real objects do not radiate as much heat as a perfect black body. They radiate less heat than a black body and are called gray bodies. To take into account the fact that real objects are gray bodies, Equation 2 is modified to be of the following form.

Q = ε σ A T⁴

Where:

ε = emmissivity of the grey body (dimensionless)

Emissivity is simply a factor by which we multiply the black body heat transfer to take into account that the black body is the ideal case. Emissivity is a dimensionless number and has a maximum value of 1.0.

Emissivity of Surface Table gives the emittance of various surfaces and emphasizes the variation possible in a single material. The values in the table apply, with a few exceptions, to normal radiation from the surface.

Surface	Temp * C°	Emissivity *
Metals and their oxides
Aluminum:
Highly polished	230–580	0.039–0.057
Polished	23	0.040
Rough plate	26	0.055–0.07
Oxidized at 600°C	200–600	0.11–0.19
Oxide	280–830	0.63–0.26
Alloy 75ST	24	0.10
75ST, repeated heating	230–480	0.22–0.16
Brass
Highly polished	260–380	0.03–0.04
Rolled plate, natural	22	0.06
Rolled, coarse-emeried	22	0.20
Oxidized at 600°C	200-600	0.61–0.59
Chromium	40–540	0.08–0.26
Copper
Electrolytic, polished	80	0.02
Comm’l plate, polished	20	0.030
Heated at 600°C	200–600	0.57–0.57
Thick oxide coating	25	0.78
Cuprous oxide	800–1,100	0.66–0.54
Molten copper	1,080–1,280	0.16–0.13
Dow metal, cleaned, heated	230–400	0.24–0.20
Gold, highly polished	230–630	0.02–0.04
Iron and steel:
Pure Fe, polished	180–980	0.05–0.37
Wrought iron, polished	40–250	0.28
Smooth sheet iron	700–1,040	0.55–0.60
Rusted plate	20	0.69
Smooth oxidized iron	130–530	0.78–0.82
Strongly oxidized	40–250	0.95
Molten iron and steel	1,500–1,770	0.40–0.45
Lead:
99.96%, unoxidized	130–230	0.06–0.08
Gray, oxidized	24	0.28
Oxidized at 190°C	190	0.63
Mercury, pure clean	0–100	0.09–0.12
Molybdenum filament	730–2590	0.10–0.29
Monel metal, K5700
Washed, abrasive soap	24	0.17
Repeated heating	230–875	0.46–0.65
Nickel and alloys:
Electrolytic, polished	23	0.05
Electroplated, not polished	20	0.11
Wire	190–1,010	0.10–0.19
Plate, oxid. at 600°C	200–600	0.37–0.48
Nickel oxide	650–1,250	0.59–0.86
Copper-nickel, polished	100	0.06
Nickel-silver, polished	100	0.14
Nickelin, gray oxide	21	0.26
Nichrome wire, bright	50–1,000	0.65–0.79
Nichrome wire, oxide	50–500	0.95–0.98
ACI-HW (60Ni, 12Cr); firm black ox, coat	270–560	0.89–0.82
Platinum, polished plate	230–1,630	0.05–0.17
Silver, pure polished	230–630	0.02–0.03
Stainless steels:
Type 316, cleaned	24	0.28
316, repeated heating	230–870	0.57–0.66
304, 42 h at 520°C	220–530	0.62–0.73
310, furnace service	220–530	0.90–0.97
Allegheny #4, polished	100	0.13
Tantalum filament	1,330–3,000	0.194–0.33
Thorium oxide	280–830	0.58–0.21
Tin, bright	24	0.04–0.06
Tungsten, aged filament	25–3,320	0.03–0.35
Zinc, 99.1%, comm’l, polished	230–330	0.05
Galv., iron, bright	28	0.23
Galv. gray oxide	24	0.28
Refractories, building materials, paints, misc.
Alumina	260–680	0.6–0.33
Alumina, 50-mm grain size	1,010–1,570	0.39–0.28
Alumina-silica, cont’g	1,010–1,570
0.4% Fe₂O₃	-	0.61–0.43
1.7% Fe₂O₃	-	0.73–0.62
2.9% Fe₂O₃	-	0.78–0.68
Al paints (vary with amount of lacquer body, age)	100	0.27–0.67
Asbestos	40–370	0.93–0.95
Calcium oxide	750–1,100	0.29–0.28
Candle soot; lampblack-waterglass	20–370	0.95 6 0.01
Carbon plate, heated	130–630	0.81–0.79
Ferric oxide (Fe₂O₃)	500–900	0.8–0.43
Magnesium oxide, 1 µm	260–760	0.67–0.41
Oil layers
Lube oil, 0.01 in on pol. Ni	20	0.82
Linseed, 1–2 coats on Al	20	0.56–0.57
Rubber, soft gray reclaimed	24	0.86
Silica, 3 µm	260–740	0.7–0.5
Misc. I: shiny black lacquer, planed oak, white enamel, serpentine, gypsum, white enamel paint , roofing paper, lime plaster, black matte shellac	21	0.87–0.91
Misc. II: glazed porcelain, white paper, fused quartz, polished marble, rough red brick, smooth glass, hard glossy rubber, flat black lacquer, water, electrographite	21	0.92–0.96

* When two temperatures and two emissivities are given they correspond, first to first and second to second, and linear interpolation is suggested.

Reference: Marks Standard Handbook for Mechanical Engineers